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Researchers at the University of California, Berkeley, are trying to make the process of making blue jeans more environmentally friendly. They engineered bacteria to produce the indigo dye that gives jeans their unique color.
“Unfortunately, indigo dyeing of denim is a very polluting process,” said John Dueber, a professor of bioengineering and co-lead of the study. Their research was recently published in the journal Nature Chemical Biology.
The blue color of jeans comes from indigo-dyed yarn.
Transformed E. coli
A cleaner method for indigo synthesis
The vast majority of jeans are dyed with synthetic indigo, a dye that mimics the dye extracted from the Indigofera plant. The synthesis of indigo dye requires a variety of toxic chemicals, including formaldehyde, as does the dyeing process. This creates a huge amount of pollution. In some parts of the world, rivers near denim factories turn blue, poisoning and killing fish and affecting the health of workers and residents. With more than 40,000 tons of indigo dye produced each year, pollution caused by indigo has become a serious problem.
The team is trying to develop an indigo dye that reduces the chemicals required in the synthesis process and does not require so many chemicals to be added during the dyeing process.
“To make this new dye, we drew inspiration from the way plants naturally synthesize indigo. The research team modified a type of E. coli to become a “chemical factory” that produces indigo precursors. This precursor It is stable and can be stored until needed. Traditional synthetic indigo requires chemical processing to reduce and dissolve the indigo dye so that it can be precipitated on the cotton fiber. The precursor produced by E. coli is different. It only requires An additional enzyme. The final product is “exactly the same” as traditional synthetic indigo, Diebel said.
This scarf is dyed with indigo produced by E. coli.
Market oriented
The dilemma from laboratory to mass production
For bacterially produced indigo to reach the mass market, two major problems must be overcome, Diebel said. First, indigo dyes best at a high pH, with most denim factories using a pH of around 10.5. But the enzyme Dibel’s team used in the process was only effective at a pH of 8. So now the team is working on tweaking the enzyme so it can react at a higher pH. The second issue is to expand production scale.
“We are very confident that we can scale this method up,” Diebel said, “but there is always a lot of work to be done to get from laboratory scale to industrial production.”
The indigo produced by this bacterium could be used in the production of small-scale custom jeans in a few years. There’s an urgent need for better production processes, Diebel said.
“Now that many countries that produce denim fabrics are beginning to consider environmental management measures, there may be more pressure to force these areas to adopt new production processes.
Pollution has not been solved
The washing and distressing step is still producing dirty water
Peter Hauser is a retired textile engineering professor from North Carolina State University who studied indigo dye. He agreed with Dibel’s point of view, but he believed thatTechnologies like those developed by Diebel’s team cannot solve all problems.
Hauser believes that a lot of the contamination that occurs in denim manufacturing comes from rinsing after dyeing and sanding for the distressed effect. Denim, even if it is dyed with indigo produced by bacteria, can still produce dirty water when washed.
“Once applied, the indigo produced by this bacterium causes no less pollution than it would have otherwise,” Hauser said.
Some eco-conscious manufacturers are returning to natural indigo dye, which reduces chemical use but has long been shunned for cost and yield reasons. In Tennessee, the United States, a company called Stony Creek Colors began to encourage farmers to grow indigo to replace tobacco, hoping for a renaissance of natural indigo. But even if it is natural indigo, the washing process during manufacturing will still pollute the water body.
Another solution is to not dye your jeans with indigo at all. Most dyes will actually penetrate the fiber, but indigo just sticks to the surface of the yarn, which is why rinsed indigo runs into the water. This is also why jeans turn white with wear. While other dyes can produce denim blue, they don’t offer the unique and sought-after whitening effect that indigo does.
“Indigo is actually a terrible dye,” Hauser said, “but people like indigo so much because of its special properties—it lightens and washes out.”
